Green tea is hot. You can buy a bottled green tea beverage just about anywhere these days. And food manufacturers are adding green tea or its extracts to everything from coffee to juice drinks.
How good is the evidence regarding the benefits of green tea and your health? Studies in laboratory animals are impressive, but compelling evidence in humans has been hard to come by.
Drinking tea regularly may be one of the most practical lifestyle changes you can make to significantly reduce your risk of suffering a stroke,” says epidemiologist Lenore Arab of the University of California at Los Angeles. Arab co-chaired the Fourth International Scientific Symposium on Tea and Human Health in 2007.
She and her colleagues pooled the results from 10 studies—of nearly 200,000 people in China, Japan, Finland, the Netherlands, Australia, and the United States— that looked at tea consumption and stroke risk. (The meta-analysis was funded by Unilever, which owns Lipton.)
“The benefit of drinking tea came shining through no matter where people lived in the world,” says Arab. Those who drank at least three cups every day had a 21 percent lower risk of suffering a stroke compared with those who drank less than a cup a day.
“There’s a strong association, but we don’t know if there’s something about the people who drink tea that would account for their having fewer strokes,” explains Rachel Johnson, a professor of nutrition at the University of Vermont and a spokesperson for the American Stroke Association.
What’s needed, she says, is a trial that randomly assigns people to drink either tea or an indistinguishable tea-free placebo.
The evidence that green tea can prevent prostate cancer is not very encouraging. In four studies that followed more than 95,000 men in Japan and Hawaii for 7 to 20 years, those who drank the most tea had no lower overall risk of being diagnosed with prostate cancer than those who drank the least. A recent review by the American Institute for Cancer Research and the World Cancer Research Fund found too little evidence to draw any conclusions about whether tea — green or black — can prevent prostate cancer.
But for men with—or at high risk of—prostate cancer, the benefits of green tea may make a difference, suggests researcher Susanne Henning of the Center for Human Nutrition at the University of California at Los Angeles.
She and her colleagues recently studied 93 men diagnosed with prostate cancer who drank six cups of green tea, black tea, or water for three to eight weeks before their prostates were removed. The men who drank green tea had lower levels of a biomarker involved in the regulation of cell proliferation and apoptosis (cell death). They also had slightly lower PSA levels.
“I would definitely advise men with prostate cancer to drink large amounts of green tea, because it may slow down the progression of the disease,” she said.
“Cohort studies that follow women for years really do not show any protective effect from drinking tea on the risk of developing breast cancer,” says Anna Wu, co-leader of the Cancer Control Research Program at the University of Southern California’s Keck School of Medicine in Los Angeles.
In the six studies that tracked more than 140,000 women in Japan, Sweden, the Netherlands, and the United States for up to 24 years, those who reported drinking the most tea were no less likely to be diagnosed with breast cancer than those who drank the least tea.
But there may be benefits of green tea for women who already have breast cancer.
In two studies of Japanese women who had been diagnosed with breast cancer, those who drank more than three cups of green tea every day had a 27 percent lower risk of having their cancer recur than those who drank little or no green tea.
“Regular tea drinkers may experience a different rate of cognitive decline than non-tea drinkers,” says UCLA epidemiologist Lenore Arab.
Arab and her colleagues analyzed data from the Cardiovascular Health Study, which has been tracking heart disease and stroke rates in adults 65 years of age and older in North Carolina, California, Maryland, and Pennsylvania since 1989.
More than 4,800 of the study participants took a yearly Mini-Mental State Examination (MMSE)—a questionnaire that is used to screen for memory loss and other cognitive impairment.
Those who drank tea—green or black— at least five times a week had about a 30 percent slower rate of decline in their scores than those who didn’t drink tea at all. But so did those who drank tea just one to three times a month. So it’s not clear whether tea, rather than something else about tea drinkers, protects the brain.
If there are any health benefits of green tea —and that’s a big “if”— how much of what you drink may matter. “Consume enough of the tea polyphenols and consume them often enough—that means three or more servings a day—to keep their levels in your blood high,” recommends Purdue University polyphenols researcher Mario Ferruzzi.
The best source of tea polyphenols: brewed green tea.
To get the benefits of green tea, “Make sure you drink a proper cup, not some weak ready-to-drink or instant tea product that has maybe a third or less of what’s in brewed tea,” says Ferruzzi.
Steep the tea bag or tea leaves for at least three minutes, suggests tea researcher Claudia Fajardo-Lira of the University of California at Northridge. “It takes time for the polyphenols to dissolve into the water.”
Squeezing in some lemon helps, since it supplies vitamin C, which protects the polyphenols from being oxidized and lost.
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